Around one in four women are obese and doctors are increasingly dealing with more complicated pregnancies and births due to the effects of being overweight.

Obesity surgery is one of the most effective long-term methods for substantial weight loss but women should be warned that complications from the operation can cause problems in pregnancy, doctors said.

In a review in the journal The Obstetrician & Gynaecologist doctors said that pregnancy after obesity surgery is safer than still being morbidly obese while carrying a child with almost eight in ten women having no complications.

However a study has found that of women who have had a gastric band fitted to reduce the amount of food the stomach can hold, one in four suffered complications resulting in severe vomiting.

Another found the miscarriage rate within 18 months of weight loss surgery was twice that of pregnancies more than 18 months after the operation, 31 per cent compared with 18 per cent.

The review also recommends that women should receive advice and information preconception on topics such as contraception, nutrition and weight gain and vitamin supplementation.

"In light of current evidence available, pregnancy after bariatric surgery is safer, with fewer complications, than pregnancy in morbidly obese women.

"However, this group of women should still be considered high risk by both obstetricians and surgeons.

“Increasingly, obstetricians, surgeons and primary care clinicians will be required to address questions posed by their patients regarding the safety of pregnancy after weight loss surgery.”

TOG’s Editor-in-Chief, Jason Waugh said: “Pregnancy after bariatric surgery is safer than pregnancy in morbidly obese women. Women who have had bariatric surgery generally tolerate pregnancy well. However, there are risks involved and patients must be well informed.

“Optimal education should be encouraged in these individuals so that they can make well informed decisions about planning pregnancy after their surgery.”